None.
Not Applicable.
The present invention is directed to a closed loop control apparatus and method for controlling, without operator input, the operation of a grinding mill system where its output or sizing (grind) is connected to a process such that a process flow requirement can be matched by the output at a substantially constant level.
In the past, material feeders connected to grinding mills, such as roller mills, have .been traditionally controlled by measuring one or more variables, such as the relative pressure differential across the roller mill, and using the differential as a target control means for the feeder to the roller mill. An example of such prior art is found in U.S. Pat. No. 4,602,744 to Williams for a xe2x80x9cMethod of Controlling A Grinding Roller Millxe2x80x9d which monitors the differential pressure as a safety net for modulating the rate of fuel feed into a grinding mill with notice to an operator when the system needs to be adjusted either by altering the material feed rate, synchronizing the feed rate or grinding capabilities, by altering the centrifugal crushing force by changing the mill speed, thereby yielding a substantially constant material flow to an associated burner receiving the ground fuel.
A similar control system can be found in U.S. Pat. No. 5,611,494 to Williams for a xe2x80x9cIsolated Intelligent And Interrelated Control System With Manual Substitutionxe2x80x9d which discloses a boiler fuel distribution control system in which a boiler fuel demand signal is employed to regulate isolated control components to control the rate of grinding of fuel within predetermined limits of air supply. The grinding of the fuel in the ""494 Williams patent is accomplished at a desired mill grinding speed and within a fluid bed differential pressure across the grinding mill to maintain a supply of fuel adequate to keep up the desired boiler burning rate of solid fuel. The system of the ""494 Williams patent further provides for temporary manual adjustment to the individual isolated control components in the event of a fault in the automated control circuits of the system.
These known examples of prior art are suitable for use with direct fired boilers systems where service personnel or operators are standing by on a continual basis to either respond to a signal requesting a change in the fuel feed rate, or to take over manual control of a component in the event of automatic controller failure. Accordingly, it has come to be desirous to have a closed loop feedback control system implemented in software which can be readily adapted to regulate the rate of a material flow through a wide variety of grinder / processor systems, and which does not rely on the presence of an operator to change settings or manually control individual components, and which can automatically compensate for work index, guidability changes, moisture changes, different feed materials, or fineness of grinds by adjusting the operational parameters automatically for the remaining components and control value settings.
Briefly stated, in its broad aspect the system of the present invention includes a control processor configured with software to monitor a number of important variables for the regulation or flow of the material feed to a grinding mill system, so as to maintain or match the output flow requirements from an associated process by matched rate or desired fineness. Monitored variables include mill speed, mill differential pressure, spinner speed, component motor current draw, air flow, and air temperature. The system software is configured to linearly interpolate variables between predetermined set points for the monitored variables. The predetermined set points are stored in register tables, and may be altered by an operator from a remote location, or in response to a change in the desired materials or fineness product. In the event a variational change is detected in one or more monitored variables, the system calculates one or more new variable setting, and makes the appropriate adjustments without the need for operator intervention.
In addition to providing a control processor with monitoring software, the system of the present invention is configured to track the variable inputs over time, maintaining at least one log which may be recalled in the event of a system or component failure. Furthermore, the system may be accessed from a remote location to allow for monitoring and for the alteration of the predetermined set points of individual variables, the rate at which the system samples and records the variable data, and the speed with which alterations occur.
The present embodiment additionally includes a method of operation which is set forth in more detail in the following description. The foregoing and other objects, features, and advantages of the invention as well as presently preferred embodiments thereof will become more apparent from the reading of the following description in connection with the accompanying drawings.